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Flexible versus rigid retaining structures
Short answer
Rigid structures rely on mass and base friction for stability against overturning and sliding, using triangular earth pressures and checking bearing capacity. Flexible structures like sheet piles bend, redistribute earth pressures, and stability depends on embedment depth, passive resistance, and anchors; deformation analysis requires checking deflection based on pile stiffness and anchor level.
In what respects does the design of a flexible retaining structure vary from that of a rigid retaining structure (in terms of stability and deformation analysis)?
| Point | Rigid retaining structure (gravity/cantilever wall) | Flexible retaining structure (sheet pile, anchored bulkhead) |
|---|---|---|
| Behaviour | Moves as a rigid body (rotation or sliding); bending is small | Bends (deflects) under the soil load; the deflection is part of the support |
| Earth pressure | Triangular active pressure from Rankine/Coulomb | Pressure is redistributed by arching and wall deflection; simplified (net pressure) diagrams are used |
| Stability analysis | Overturning, sliding, bearing capacity, tension at the base | Depth of embedment by moment equilibrium (free-earth/fixed-earth), anchor force, passive resistance in front |
| Structural design | Mass (gravity) design, or design of the stem and slab; the section is stiff | Maximum bending moment in the pile and the required section modulus (for sheet piles); anchor and wale design |
| Support | Weight and base friction | Passive resistance of the embedded portion, and anchors/struts |
| Deformation analysis | Small deformations; mostly checked for settlement and tilt | Deflection and movement of the retained ground must be checked; they depend on the pile stiffness and the anchor level |
✓ Answer checked by Claude Sonnet 5.5
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